Click on the three dots in the upper-right corner of the web page and then "Delete MyFRITZ! Account".

Solve the CAPTCHA.

Enable the option "Yes, I would like to delete my MyFRITZ! account" and click the button "Delete MyFRITZ! Account".

Now your MyFRITZ! account with AVM has been completely deleted.

If the MyFRITZ! account you deleted is still configured in a FRITZ!Box, you can disable it in the user interface under "Internet > MyFRITZ! Account". If you would like to set up a new MyFRITZ! account in the FRITZ!Box, simply overwrite the user account information for the old MyFRITZ! account with the account information for the new account.

If you no longer use MyFRITZ! at all and want to completely delete the MyFRITZ! account instead of just deactivating it in the FRITZ!Box, load the FRITZ!Box's factory settings.